Scalable immersed-filtration method and apparatus

ABSTRACT

A method and apparatus for filtering a large volume fluid intake system using a modular immersed-filtration array that can be easily scaled for use in a wide variety of immersion filtering applications. The immersed-filtration array is composed of a plurality of individual filtration modules. Each filtration module has a mating end that allows the module to be coupled with a base unit or plenum via a common interface port located on the base unit. The array can be scaled in a plurality of ways.

FIELD OF THE INVENTION

The present invention relates to filtration systems, and moreparticularly to filtration systems at a large volume of fluid intake.

BACKGROUND OF THE INVENTION

Large volume fluid intake systems are used for generating hydroelectricpower, providing cooling water for manufacturing and power generationplants, providing irrigation and potable water supplies, and providingsource water for desalinization plants. In the U.S. alone, these systemstake in more than 200 billion gallons of fluid per day. Unfortunately,according to U.S. Environmental Protection Agency (EPA) estimates, thesefluid intake systems remove billions of aquatic organisms from the waterbodies in which they are used, including fish, crustaceans, shellfish,sea turtles, marine mammals, as well as a plethora of other aquatic lifeforms.

Eggs and larvae of fish (commonly referred to as ichthyoplankton) areparticularly sensitive to large volume fluid intake systems because theyhave little or no swimming ability. Ichthyoplankton range in size fromabout 0.5 mm to greater than 1 mm in diameter, and normally reside inthe upper 200 meters of the water column, where they drift passively inthe prevailing currents.

Fluid intake systems negatively impact aquatic life in two major ways:entrainment and impingement. Entrainment is the circumstance where anaquatic organism is drawn into the intake system and subjected to thephysical, mechanical, chemical, and thermal forces particular to thedesign and function of the fluid manipulation system in question.Impingement describes the circumstance where an aquatic organism istrapped against an upstream physical barrier by the force of fluid flowentering the intake system, and usually occurs in situations where theintake system is screened. Most large volume fluid intake systems arescreened to prevent entrainment of debris.

Mortality rates of ichthyoplankton that are either entrained or impingedis high, and may approach 100%. To minimize the impact of large volumefluid intake systems on aquatic ecosystems, Section 316(b) of the CleanWater Act mandates that large volume fluid intake systems, such as thewater intake systems used in cooling power plants, reduce impingementlevels by 80-95% and entrainment levels by 60-90%. EPA estimates suggestthat Section 316(b) compliance will result in benefits to recreationaland commercial fishing industries in excess of $100 million annually.Additionally, Section 316(b) compliance is likely to have a beneficial,although difficult to quantify, environmental effect by creatinghealthier and more robust aquatic ecosystems.

Rates of entrainment and impingement are affected by many factors. Forexample, both entrainment and impingement are affected by the pore sizeof the apparatus used to screen the intake system. There is a linearrelationship between entrainment and pore size (i.e. entrainment ratesincrease as filter pore size increases), while there is an inverserelationship between impingement rates and pore size (i.e. impingementrates increase as filter pore size decreases).

Entrainment and impingement rates are also affected by several otherfactors including, but not limited to, the velocity of the fluid intakesystem (V_(i)) and the velocity of the source water body (V_(w)) thatserves the fluid intake system. Under most circumstances, V_(i) has aconstant value within the fluid intake system that is determined eitherby gravity or a pump. However, at the point of fluid intake, V_(i)interacts with the source water body in a complex manner whereby thevalue of V_(i) decreases with distance (d) from the point of fluidintake. As d increases relative to the point of fluid intake, it can berecognized that d will eventually reach a critical distance (d_(max))where V_(i) is equal to V_(w). In other words, an object in the sourcewater body located outside of the d_(max) area is not influenced by thefluid intake system because it is under the control of the velocity ofthe source water body flow (V_(w)). Generally, V_(w) will be constantover short time intervals, but may vary significantly over longerperiods of time as a result of a variety of environmental factors (forexample, tide, weather, rain, season, etc.).

The probability (p) of an object being entrained/impinged by a filterassociated with a fluid intake system is related in a complex manner tothe interactions between d, V_(i), and V_(w). Generally, p is expectedto be low if the ratio of V_(w)/V_(i) is high. In other words, thelikelihood of being entrained/impinged is low if the velocity of thesource water body is significantly faster than the velocity of waterbeing drawn into the fluid intake system, because a high ratio of V_(w)to V_(i) has the effect of decreasing the value of d_(max) so there is asmaller distance from the point of intake origin at which V_(i) canexert an effect that is stronger than V_(w). In this situation,entrainment/impingement is likely to occur only if an object happens topass very close to the opening of the fluid intake system.

There are few examples of anti-entrainment/impingement solutions in theart. U.S. Pat. No. 6,051,131 and U.S. patent application Ser. No.0,227,962A1 recite the use of wire screens wrapped around an intakesource, or slots in an intake pipe, to attempt to filter aquatic lifeforms from the intake fluid. Disadvantageously, these systems are proneto clogging, and require frequent and costly upkeep to maintain theirintake function. U.S. Pat. No. 7,118,307 recites the use of intake pipescovered in wire screens and buried under a natural bed of sand locatedbelow the intake fluid source to provide a two pass screening system.Disadvantageously, this system is labor intensive and costly to install,as well as difficult to maintain.

U.S. Pat. No. 5,580,454 (hereafter the “'454 patent”, incorporated byreference herein) discloses a filter cartridge that is backwashable andmay provide aspects of a filter element suitable for screening largevolume fluid intake systems. However, the filter cartridge of the '454patent was not heretofore used in such a fluid intake filteringapplication. On the contrary, the filter cartridge of the '454 patentwas designed as an in-line filter for use in high pressure applications;consequently, it has aspects that are not suited for use in screeninglarge volume fluid intake systems. For example, the filter cartridge ofthe '454 patent was designed for use within a sealed, pressurized vessel(FIG. 1A, 22), and has mounting flanges specific for this type ofin-line application (FIG. 1, 24). Additionally, because of the highpressures involved in this filtering application (and correspondinglyhigh values of V_(i)), the mounting flanges contain narrow diameterfluid connectors for moving the filtrate between the two chambers of thevessel (FIG. 1, 26), and such connectors would not be suitable for anapplication using lower values of V_(i) (e.g. cooling water intake for apower plant).

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for filtering alarge volume fluid intake system using a modular immersion filtrationarray that can be easily scaled for use in a wide variety of immersionfiltering applications. The immersed-filtration array is composed of aplurality of individual filtration modules. Each filtration module has amating end that allows the module to be coupled with a base unit orplenum via a common interface port located on the base unit. The arraycan be scaled in a plurality of ways. For example, the number of commoninterface ports on the plenum or base unit can be increased to allow acorresponding increase in the number of filtration modules. In anotherembodiment, the number and configuration of base units can be increasedto allow increases in flow-through and filtration capacity that varieswith the number of filtration modules per plenum.

The filtration module comprises a plurality of filter elements (such as,for example, those described in the '454 patent) that are assembled ontoa stacking core to create a filter stack. Generally, each filter elementcomprises an outer filtration portion connected, via a plurality oftabs, to a mounting portion having an inner cavity and an outer arcuatesurface, where the plurality of tabs, the outer arcuate surface of themounting portion, and the inner surface of the filtration portion areconfigured to form a plurality of integral fluid channels.

The filter stack is sandwiched between a first end and a second end ofthe stacking core. The first end comprises an outer circumference andbottom side which form a mating surface to couple the filtration moduleto a common interface port of a plenum. An abutment side of the firstend forms a base against which the filter stack abuts. The interior ofthe first end is hollow and the top side contains a plurality ofcavities. In the column of stacked filter elements disposed on thestacking core, the plurality of integral fluid channels accommodate theflow of filtrate from the filter stack, through the cavities in the topside of the first end of the stacking core, and out the bottom side ofthe first end of the stacking core, thereby allowing the filtrate totraverse the plenum to which the filtration module is attached andmoving the filtrate into the general fluid intake system. The second endof the stacking core is affixed with an adjustable compression meansthat provides counter-pressure to hold the filter stack against the topside of the first end of the stacking core.

The adjustable compression means allows the filter stack to bebackwashed by reversing the flow of fluid through the filter stack. Thepressure generated by this counter flow reduces the pressure applied tothe filter stack by the compression means, thereby allowing the filterelements within the stack to separate as fluid flows from the interiorto the exterior of the stack, removing any impinged material from theoutside of the stack in the process. The stacking core is rigid enoughto withstand high radial forces and the integral passages reduce thepotential for preferential flow of backwash fluid. Avoidance ofpreferential flow is a significant feature that ensures uniformity offlow of backwash fluid throughout the filter elements in the stack,which ensures even cleaning of the individual filter elements in thefilter stack.

An advantage of the filtration module of the present invention is itsmodular design, which allows it to be incorporated into any conceivabletwo or three dimensional configuration that could be designed for afluid intake system. Additionally, this modular design allows thepresent invention to be easily scaled up or down to suit essentially anylarge volume fluid processing system. Yet another advantage of themodular, scalable nature of the present invention is that it can beeasily incorporated into a wide variety of different filtration arrayarchitectures to accommodate almost any imaginable physical location ofa fluid intake system.

Another advantage of the filtration module of the present invention is ahigh ratio of surface area to three dimensional volume, which allows arobust level of fluid processing capacity at a low velocity of fluidintake (V_(i)). This is advantageous in the context of animmersed-filtration array incorporating the present invention because itreduces ichthyoplankton entrainment/impingement rates by maintaining afavorable ratio of V_(w) to V_(i), thereby reducing the probability ofichthyoplankton proximity to the point of intake.

Advantageously, the filtration module of the present invention virtuallyeliminates ichthyoplankton entrainment rates because the filter elementgrooves are sized in the micron range, while the lower limit ofichthyoplankton diameter is about 0.5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

The features and advantages of the present invention will be betterunderstood when reading the following detailed description, takentogether with the following drawings in which:

FIG. 1A is an elevation view of a filter vessel including a plurality offilter cartridges according to the prior art;

FIG. 1B is a top view of a perforated filter plate supporting filtercartridges in the prior art filter vessel of FIG. 1A;

FIG. 1C is a side section view of the perforated filter plate of FIG. 1Bshowing a tube clamp fastening implementation according to the priorart;

FIG. 2A is an exploded view of an exemplary filtration module includinga stacking core, a single filter element, and a compression meansaccording to the invention;

FIG. 2B is a perspective view of the mating end of the stacking coredepicting the mating surface and the conduit for filtrate flow of thefiltration module of FIG. 2A;

FIG. 3 is a side view of a filtration module depicting the assembledfilter stack affixed to the stacking core via the compression meansaccording to the invention;

FIG. 4A is a plan view of a filtration element according to the priorart;

FIG. 4B is a perspective view of a partial stack of filter elementsaccording to the prior art; and

FIGS. 5A-5E, FIGS. 6A-6D, FIGS. 7A-7B and FIGS. 8A-8D are views of athree dimensional immersed-filtration array according to the invention.

DETAILED DESCRIPTION

As illustrated in FIGS. 2-5, an immersed-filtration apparatus accordingto the invention is comprised of at least one filtration module, whichin turn is comprised of a plurality of stacked filter elements. Asgenerally illustrated in FIG. 2A, the filtration module is comprised ofa geometric stacking core (42), which holds a plurality of filterelements (46) to form the filter stack (FIG. 3, 62). The stacking core(FIG. 4A, 42) has a geometric shape that corresponds to the inner cavityof the filter element (FIG. 4B, 70), a mating end (FIG. 2A, 40)comprising a mating surface (FIG. 2A, 47) and a conduit for filtrateoutflow (FIG. 2A, 49), and a second end comprising an attachment means(44) for affixing a compression means (48).

As depicted in FIG. 4B, the filter elements are 1½″ wide and generallyconstructed and configured as described in the '454 patent, consistingof an outer filtration portion (72) and an inner geometrically shapedcavity (70) connected to one another via a plurality of tabs (74). Theinner geometrically shaped cavity contains both an inner (79) and outer(80) side, and functions to allow the filter element to fit onto thecentral shaft of the stacking core in a manner that prevents rotation ofthe element around the shaft (i.e. it resides in a fixed two dimensionalplane once positioned on the stacking core). The plurality ofinterstices (76) that reside between the outer filtration portion (72),the outer side of the inner geometric cavity (80), and the tabs (74)form a plurality of integral fluid connectors (FIG. 4A, 76) once theindividual filter elements are combined to form the filter stack (FIG.3, 62).

As shown in FIG. 4B, the outer filtration portion (72) is formed bytwelve arcs (84) that contain a plurality of grooves (82) that span thewidth of the outer filtration portion (72). The twelve arcs (84)function to increase the surface area of the outer filtration portion(72), which in turn increases the total number of grooves (82)permeating the perimeter of the outer filtration portion (72). Thegrooves (82) possess about the same three dimensional characteristics asdescribed in the '454 patent, but in the exemplary embodiment are sizedat about 40 microns.

In the exemplary embodiment, the stacking core is 7¾″ tall and consistsof a single piece of injection molded glass-filled polypropylene.However, one could easily construct the stacking core with differentdimensions, or from different thermoplastic compositions, to suitdifferent filtration applications. As illustrated in FIG. 2A, the matingend (40) of the stacking core is wider than the stacking core (42). Thetop side (41) of the mating end serves as the base against which thefilter stack abuts, and also contains a plurality of cavities (FIG. 2B,45) that align with the integral fluid connectors of the filter stack(FIG. 4A, 76). The outer circumference of the first end located belowthe top side (41) functions as a mating surface (47), and while in thisexemplary embodiment the mating surface is a 1¼″ National Pipe Thread(NPT) fitting, one skilled in the art can appreciate the potential forany of a variety of additional or alternative mating means. The regionof the mating end interior to the mating surface in the illustrativeembodiment forms a conduit for filtrate flow (49) through the pluralityof cavities present in the top side of the first end (FIG. 2B, 45). Incombination, the conduit (49) and the plurality of cavities (45) form apassageway for moving filtrate from the filter stack through the firstend of the stacking core.

As generally illustrated in FIG. 2A, the second end of the stacking coreis threaded (44) to allow attachment of a compression means (48). Whilethe second end is threaded in this exemplary embodiment, it should beappreciated that a plurality of additional means for attaching thecompression means could also be used. Generally, the compression meanscomprises a compression plate (50), a compression spring (52), ananti-torsion washer (54), and an end piece (56). The compression plate(50) sits on top of the filter stack and functions to seal the top endof the filter stack; additionally, it also provides a contact surfacefor the bottom end of the compression spring (52), which is locatedbetween the compression plate (50) and the anti-torsion washer (54). Inturn, the anti-torsion washer is located between the compression spring(52) and the end-piece (56). The compression means functions to applyadjustable pressure to the compression plate, which subsequentlycompresses the filter stack against the top side of the first end. Whilethis represents an exemplary embodiment, it should be appreciated thatvarious other means for providing adjustable pressure against the filterstack could also be implemented according to the present invention.

An embodiment of an immersion filtration array according to theinvention, is illustrated in FIGS. 5A-5E, and comprises a plurality offiltration modules (28) affixed to a base (90) via a correspondingplurality of common interface ports (92). In this exemplary embodiment,the immersion filtration array is a three-dimensional box (96) forming aplenum or base unit with a filtration module containing base (90)affixed to at least one surface of the box and a second filtrationmodule containing base affixed to the bottom surface of the box (96).The common interface ports (92) are threaded to match the threadedmating end of the filtration module (40). Additionally, the box (96)also contains an attachment means (94) for connecting it to a fluidintake system.

The immersion filtration array according to the invention by itsconfiguration is scalable. For example, the base plate (90) can beenlarged to contain more common interface ports (92), thereby resultingin a corresponding increase in the number of filtration modulesassociated with the base, as well as a proportional increase in thefiltrate through-put capacity. Alternatively, the system can be scaledby increasing the number of filtration module/base assemblies associatedwith the fluid intake system, thereby resulting in a linear doubling ofthe filtrate through-put capacity. While the exemplary embodimentdescribed herein depicts the immersion filtration array as a threedimensional box, it should be noted that it could also be a sphere orpolyhedra. Other geometries and configurations of the immersion filteraccording to the invention can be implemented, such as those illustratedin FIGS. 6A-6D, FIGS. 7A-7B and FIGS. 8A-8D.

The modular nature of the immersion filtration array according to theinvention provides for a high filtrate through-put capacity at arelatively low velocity of fluid intake (V_(i)). In the exemplaryembodiment, V_(i) is equal to about 0.2 feet per second and generates afiltrate through-put rate of about 9.25 gallons per minute perfiltration module. Even if the immersed-filtration array is implementedin a source water body that has a relatively low main water velocity(V_(w)) of 1.1 feet per second, the array can still achieve anentrainment/impingement reducing ratio of V_(w) to V_(i) that is about5.5. Given this, the immersed-filtration array can reduceentrainment/impingement rates by maintaining an optimal ratio of V_(w)to V_(i) while simultaneously maintaining an acceptable level offiltrate through-put capacity for a large volume fluid intake system.

Although the invention has been shown and described with respect to anexemplary embodiment thereof, it will be appreciated that the foregoingand various other changes, additions, and omissions in the form anddetail thereof may be made therein without departing from the spirit andscope of the invention.

1. A scalable filtration array for immersion in fluid containingichthyoplankton, comprising: a base configured to receive a plurality offiltration modules, wherein said base has common interface portsconfigured to accept a mating end of said filtration modules, and saidbase has corresponding numbers of common interface ports and filtrationmodules, and said mated common interface ports and filtration modulesform a corresponding number of fluid connectors for filtrate dischargesaid plurality of filtration modules being configured to reduceentrainment and impingement of ichthyoplankton in said fluid.
 2. Thescalable filtration array of claim 1 wherein the shape of said base isselected from the group consisting of circles, rectangles, polygons,spheres, cubes, and polyhedra.
 3. The scalable filtration array of claim1 wherein said common interface ports are threaded to allow mating ofsaid filtration modules containing a complementary threaded mating end.4. The scalable filtration array of claim 1 wherein each of said pluralsof filtration modules, comprises: a plurality of filter elements; astacking core configured to allow assembly of said filter elements intoa filter stack, wherein said stacking core has a first end configuredfor mating to a base, and a second end configured to accept an endpiece, and said filter elements form a fluid connector for filtratedischarge when said filter stack is assembled between said first end andsaid second end, and said fluid connector discharges said filtrate fromsaid first end of said stacking core, and; an adjustable compressionmeans, wherein said compression means is located between said filterstack and said cap attachment.
 5. The scalable filtration array of claim4 wherein said adjustable compression means comprises: a compressionplate that sits against said stack of filter elements; a spring thatsits against said compression plate, and; an anti-torsion washer locatedbetween said spring and said end piece.
 6. The filtration module ofclaim 1 wherein said first end is threaded to allow mating to said base.7. A method of reducing entrainment and impingement of fluid-borneichthyoplankton, the method comprising the steps of: providing animmersed filtration array; filtering fluid through a plurality offiltration modules of said immersed filtration array, wherein saidfiltration modules contain filter elements having a groove size of about10 times to about 1,000 times less than the average lower diameter limitof ichthyoplankton, and; filtering at a V_(i) such that the ratio ofV_(w) to V_(i) is between about 2 and
 25. 8. The method according toclaim 7 wherein said filter element pore size is about 40 microns. 9.The method according to claim 7 wherein the ratio of V_(w) to V_(i) isabout
 5. 10. The method according to claim 7 wherein V_(i) is about 0.2cubic feet per second.